Sutton Council has drafted in a crack team of Sussex cattle to look after the rare chalk grasslands of Roundshaw Downs.
The cattle, one of the UK's oldest breeds, will be tasked with keeping weeds and shrubs away from the borough's largest nature reserve.
It was feared the weeds could potentially overrun the downs, which is vital to harbouring wild flowers, insects and ground-nesting birds like skylarks.
The chalk grasslands are rarely found outside the south east and can support rare breeds of plants and animals such as the greater yellow rattle and meadow pipits.
Sutton Council claim mowing costs will be reduced by £2,000 a year as a result.
Councillor Jill Whitehead, chairwoman of Sutton's environment and neighbourhoods committee, said: "Sutton is very proud of its Green record and this is an innovative way of helping to preserve the borough's rare chalk grasslands.
High quality chalk grassland can support up to 50 different species of plants within one square metre and bringing in grazing cattle will help increase the amount of plants and animals that can live and flourish there.
"It's also a useful means of saving money and of bringing a little bit of the countryside into the city, and will give local children the chance to see farmyard animals right on their doorsteps."
The cattle, which will be on the Downs for three to six months, will be looked after by welfare experts from the Heritage Lottery Funded Old Surrey Downs Project and will live in a secure enclosure, which members of the public and dog walkers will be free to use.
Anyone who wants to help check the cattle, please visit firstname.lastname@example.org to find out how to get involved.
The project's set-up costs have been met by the Heritage Lottery Fund and the Downlands Countryside Management Project will continue to provide funding after the initial project is complete.
The cattle arrived on Wednesday but for the first couple of days after their journey it is best not to disturb them.
Lets take a look at the stats...
Mechanics: 32 teeth
Weight: 600 to 900kg
Length: 1.9 to 2.5 metres (6.2 to 8.2 ft)
Lifespan: 15 - 25 years
Speed: Up to 20 mph
Diet: tree leaves, grass and ferns
Hours of work: Cattle graze up to 8 hours a day, taking in about 45 kg (100lb) of feed. Cows can drink up to 35 gallons of water a day.
INTERESTING FACT - A cow stands up and sits down about 14 times a day.
LAWNMOWER (Poulan Pro PB2H54YT riding mower)
Mechanics: Briggs & Stratton Intek V-Twin
Lifespan: 2 year warranty
Speed: 5.5 mph
Diet: Anything in its way
Hours of work: Whenever you hit the button (features a cup holder for breaks)
INTERESTING FACT - the first lawnmower was invented in 1827 in Stroud, Gloucestershire, by Edwin Budding.